EP3048307B1 - Method for controlling a rotational speed of a fan - Google Patents

Description

The invention relates to a method for controlling a speed of a fan of a fan to a target speed, which is driven jointly by a first drive and a second drive, wherein the first drive is controlled and / or controlled by a first control unit and the second drive is controlled and / or controlled by a second control unit.

From the DE10219872 A1 is a fan drive with fluid friction clutch and additional electric drive known. The regulation disclosed therein is limited to the adjustment of the control deviation between the required setpoint speed and the current fan speed. As a result, the benefits of the combined fan drive can not be fully exploited.

The present invention is based on the object to provide an improved or at least other embodiment of a method for controlling a speed of a fan wheel, which is driven by two drives, which is characterized in particular by an improved efficiency.

This object is achieved by the independent claims. Advantageous developments are the subject of the dependent claims.

The invention is based on the general idea of enabling an efficiency-optimized power split between the first drive and the second drive. This is achieved by determining, based on an efficiency strategy, a first torque to be generated by the first drive and a second torque to be generated by the second drive, in each case starting from the first torque and from the second torque Torque a first virtual target speed and a second virtual target speed are determined, and that the first virtual target speed of the first control unit is supplied as an input and that the second virtual target speed of the second control unit is supplied as an input variable. The efficiency strategy divides the torque required to achieve the desired speed of the fan wheel into the first drive and the second drive such that the overall efficiency is improved. Since the generated torques are not available as a measured variable, virtual setpoint speeds are determined on the basis of the torques to be generated. These virtual target speeds are fed to the control units, which then determine the necessary control variables for the respective drives with the aid of the pilot control fields stored in the control units, and control the drives accordingly. In this way, the desired, optimized for the efficiency, power distribution between the two drives, approximately achieved. When holding the speed of the fan wheel to the target speed, the control units do not deviate significantly after a transient phase from the control variables determined on the basis of pilot control fields, so that the efficiency-optimized power distribution between the first drive and the second drive remains at least approximately even in continuous operation.

In the specification and the appended claims, a virtual speed is understood to mean a value that is used only as an auxiliary quantity. For example, virtual target speeds are values that are actually not to be reached. Accordingly, virtual actual speeds are not available in the system. The virtual speeds indicate to the control units operating conditions that are not actually present to achieve the desired torque distributions between the two drives.

A favorable possibility provides that an electric motor as the first drive and a viscous coupling are used as a second drive, which the fan coupled to a shaft of the internal combustion engine. This allows the advantages of the electric motor and the viscous coupling to be well combined. In particular, the high dynamics of the electric motor can be used to allow rapid achievement of the desired speed. Furthermore, the efficiency characteristics of the two drives are different, so that an optimization of the overall efficiency can be achieved by a power distribution between the two drives. For example, at an operating point at which one drive is more efficient, it takes over the drive of the fan wheel entirely or at least to a greater extent than the other less efficient drive.

A further favorable possibility provides that the torques to be generated by the first drive and by the second drive are determined by the efficiency strategy on the basis of a desired rotational speed of the fan wheel and / or a rotational speed of a shaft of the internal combustion engine. The efficiency of the viscous coupling is dependent, inter alia, on the difference between the rotational speed of the shaft of the internal combustion engine and the rotational speed of the fan wheel, for example, the slip power of the viscous coupling is greater at high differences, so that the efficiency of the viscous coupling is smaller. The efficiency of the electric drive results from the efficiency chain comprising the efficiencies of the electric motor, the lines, the power amplifier of the engine control and the generator. Based on the target speed of the fan and the speed of the shaft of the engine so it can be determined in what proportion the power of the two drives must be divided to determine an optimal efficiency.

A particularly favorable possibility provides that the torques to be generated by the first drive and by the second drive through the efficiency strategy, taking into account the efficiencies of the first drive and the second drive to be determined. Thus, it is possible to optimize the overall efficiency in driving the fan wheel.

An advantageous solution provides that the first virtual setpoint speed and the second virtual setpoint speed are determined by means of a speed-torque characteristic of the fan wheel from the first torque and the second torque. On the basis of the known speed-torque characteristic, in short characteristic curve, it can be determined which speed the fan wheel would reach if the fan wheel is driven with the first or with the second torque. If this speed is used as the first setpoint speed or second virtual setpoint speed, due to the pilot control maps in the control units, the two drives which attempt to reach the virtual speeds generate just the first torque or the second torque. Thus, although the generated torques of the drives are not present as a measure, a distribution of the torques can be achieved.

A further advantageous solution provides that the first control unit and the second control unit each use a pilot control map and a PID controller. This type of control units has proven itself and allows a fast and efficient control of the speed of the fan wheel.

In the description and the appended claims, a PID controller is understood to mean a proportional-integral-derivative controller.

A particularly advantageous solution provides that the first virtual speed is used as input to the pilot map of the first control unit of the first drive and that the second virtual target speed is used as an input to the pilot map of the second control unit of the second drive. By using the virtual target speed as an input variable for the pilot control maps of the control units are from the pilot control maps just determines the control variables for the respective drives, which are necessary to achieve the virtual target speeds, so the control variables that generate the first torque and the second torque through the respective drives.

A favorable variant provides that the control deviation, which is used by the PID controllers, from a difference between the speed of the fan and the target speed of the fan wheel is determined. In this way it can be achieved that the control units to the correct target speed control, although the control units, the virtual speeds are supplied as an input variable.

A further favorable variant provides that the respective control deviations which are used by the PID controllers are determined from a difference between the respective virtual setpoint speed and a respective virtual actual speed. The respective virtual actual speeds are formed from the speed of the fan in the same way as the virtual target speeds from the target speed, so that at a match of the speed of the fan with the target speed and the virtual target speeds with the virtual Actual speeds match. It can thereby be achieved that the first control unit and the second control unit regulate the fan wheel to the desired desired speed.

A particularly favorable variant provides that the respective virtual actual rotational speeds are determined by subtracting an offset from the rotational speed, wherein the offset is the difference between the target rotational speed and the respective virtual target rotational speed. As a result, the virtual actual rotational speeds can be determined by simple addition or subtraction calculations. So it is only a small amount of computation necessary.

An advantageous possibility provides that the virtual actual rotational speeds are determined by multiplying the rotational speeds by a division factor, wherein the division factor is the quotient of the respective virtual target rotational speed by the target rotational speed. In this way it can be achieved that the one drive, which is to perform a lower partial power and less involved in the control of the speed of the fan wheel, as by multiplication with the division factor according to the size of the control deviation in relation to the power distribution on the each control units is divided.

An advantageous solution provides that the first control unit and the second control unit are speed control units, or that each speed control units are used as the first control unit and as the second control unit. Speeds can be measured very easily, so that the use of speed control units is cheaper to implement than the use of torque control units.

A further advantageous solution provides that the rotational speeds of the first drive and the second drive are coupled. The first drive and the second drive can not rotate independently of each other.

Furthermore, the above object is achieved by a motor vehicle with a fan, which is driven by a first drive and by a second drive, wherein a speed of at least one fan of the fan is controlled by a method as described above. The advantages of the method are thus transferred to the motor vehicle, to the above description of which reference is made.

A particularly favorable variant provides that the first drive is an electric motor and the second drive is a viscous coupling which couples the fan wheel to an internal combustion engine of the motor vehicle.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

Fig. 1

eine Prinzipskizze einer Anordnung umfassen eine Brennkraftmaschine und einen Lüfter mit einem ersten und einem zweiten Antrieb,

Fig. 2

ein Ablaufdiagramm eines Verfahrens zur Regelung einer Drehzahl eines Lüfterrades des Lüfters,

Fig. 3

eine Prinizipskizze einer Anordnung umfassend eine Brennkraftmaschine und einen Lüfter mit einem ersten und einem zweiten Antrieb, und

Fig. 4

ein Ablaufdiagramm eines Verfahrens zur Regelung der Drehzahl des Lüfterrades aus Fig. 3 gemäß einer zweiten Ausführungsform.

It show, each schematically.

Fig. 1

A schematic diagram of an arrangement comprises an internal combustion engine and a fan with a first and a second drive,

Fig. 2

a flowchart of a method for controlling a speed of a fan of the fan,

Fig. 3

a schematic diagram of an arrangement comprising an internal combustion engine and a fan with a first and a second drive, and

Fig. 4

a flowchart of a method for controlling the speed of the fan from Fig. 3 according to a second embodiment.

An in Fig. 1 Arrangement 10 includes an internal combustion engine 12 with a shaft 14. Furthermore, the arrangement comprises a fan 16 with at least one fan 17, which is used for example for cooling the internal combustion engine 12. And driven by a first drive 18 and by a second drive 20.

The first drive 18 and the second drive 20 differ, for example, the first drive is an electric motor and the second drive is a viscous coupling which couples the fan 17 with the shaft 14 of the internal combustion engine 12, so that the rotation of the shaft 14 of the internal combustion engine 12 to a Rotation of the fan 17 is transmitted.

In order to regulate a rotational speed 22 of the fan wheel 17, the first drive 18 has a first control unit 24 and the second drive 20 has a second control unit 26. The first control unit 24 and the second control unit 26 regulate the power of the first drive 18 and the second drive 20 such that the rotational speed 22 of the fan wheel 17 at least approaches a target rotational speed 28. The measurement 23 of the speed 22 can be done for example by a tachometer.

The control units 24, 26 each have a PID controller 25 (proportional-integral-differential controller) and a pilot control map 27. Furthermore, control variables 29 for the respective drives are stored in the pilot control map 27, which are necessary for certain operating points of the fan 16. For example, control variables 29 are stored for the steady-state operation as a function of the rotational speed 22 of the fan wheel 17. When setting a target speed 28 at the control units 24, 26 can be determined using the pilot control maps 27, a first good estimate for the correct control variables 29 for the drives, so that the approximation to the actual required control variables 29 can take place more quickly.

A determination 30 of the setpoint speed 28 of the fan wheel 17 takes place, for example, by an engine control unit 31, in particular based on a temperature of the internal combustion engine 12 or a temperature of a cooling medium, such as water. At high temperatures, higher target speeds are set for better cooling.

In order to achieve the best possible efficiency, an efficiency strategy 32 is applied. The two drives 18, 20 have different efficiencies, in particular different dependencies of the efficiencies, for example, on the speed or the torque to be generated. For this reason, a power distribution which is advantageous for the overall efficiency is different for different operating points. There may be different cases. In the two simplest cases, one of the drives completely takes over the driving of the fan wheel 17, while the other drive does not generate power. But there are also cases in which a division of the benefits of the efficiency is low, in which both drives contribute 18, 20 for driving the fan wheel 17.

The first drive 18 and the second drive 20 jointly drive the fan 17, so that the rotational speeds of the first drive 18 and the second drive 20 are coupled together. In particular, the rotational speeds of the first drive 18 and the second drive 20 are equal to the speed 22 of the fan wheel 17. In order to achieve a power distribution, therefore, the torque which is necessary to drive the fan 17 must be divided between the two drives. The first drive 18 must have a first torque 34 and the second drive 20 must apply a second torque 36 to bring the fan 17 to the desired desired speed 28.

For the regulation of the rotational speed 22 of the fan wheel 17, however, it is problematic because the torques 34, 36, which are generated by the two drives 18, 20, are not present as a measured variable and thus can not be used as a controlled variable.

The first torque 34 and the second torque 36 are converted into a first target virtual speed 38 and a second target virtual speed 40 and used as input to the first control unit 24 and the second control unit 26.

The determination of the virtual setpoint rotational speeds 38, 40 from the torques 34, 36 takes place with the aid of a torque / rotational speed characteristic, in short characteristic curve 41, of the fan wheel 17. This characteristic curve 41 can be derived, for example, theoretically from the geometry of the fan 16 or experimentally be determined. From the characteristic curve 41, the torques are known, which are necessary to keep the fan 17 at a certain speed. Accordingly, from the characteristic curve 41, the virtual setpoint rotational speeds 38, 40 can be determined, which would occur if the two drives 18, 20 with the first torque 34 and second torque 36 determined on the basis of the efficiency strategy 32 each drive the fan wheel 17 alone would.

The virtual speeds 38, 40 are passed as an input to the control units 24, 26. In the control units 24 and 26, the control variables 29 for the drives 18, 20 are determined with the aid of the pilot control maps 27, which are required to keep the rotational speed 22 of the fan wheel 17 at the respective virtual desired rotational speeds 38, 40. These control variables 29 cause the drives 18, 20 to determine the torques determined by the efficiency strategy 32 34, 36 generate. Thus, at the beginning of the control loop, the two drives 18 and 20 generate the first torque 34 and the second torque 36 exactly in the ratio determined by the efficiency strategy 32.

At the beginning of the control loop, a determination 42 of the control deviation 44 takes place. Since the control units 24 and 26 are supplied with virtual nominal rotational speeds 38, 40, the determination 42 of the control deviation 44 can not take place in the usual manner, since otherwise the two drives 18, 20 would each regulate to a different speed, so that the two drives 18, 20 would work against each other.

The determination 42 of the control deviation 44 therefore takes place by forming the difference between the setpoint speed 28 and the speed 22 of the fan wheel 17. The control deviation 44 is then provided to both control units 24, 26, so that the PID controllers 25 of the control units 24, 26 do not have to make their own determination 42 of the control deviation 44.

By controlling the first drive 18 and the second drive 20, the two drives 18, 20 can be removed from the operating points, which were set using the virtual target speeds 38, 40. That is, the desired power ratio determined by the efficiency strategy 32 may not be met. However, the deviations remain small, so that the arrangement 10 can still be operated close to the efficiency optimum.

Furthermore, when the setpoint speed 28 is redefined with the aid of the efficiency strategy 32, the correct power ratio is readjusted so that the deviation from the desired power ratio can be accepted for frequent setpoint speed changes. Alternatively or additionally, it can also be provided that setpoint speed 28 is set again in a specific interval is, although no change in the target speed is provided by the engine control unit.

One in the FIG. 3 and FIG. 4 illustrated second embodiment of the method for controlling the speed 22 of the fan 17 differs from that in the Fig. 1 and Fig. 2 shown in the method in that the control deviation 44 within the control units 24, 26 from a difference between the virtual target speeds 38, 40 and virtual actual speeds 46 and 48 is determined. For this purpose, the rotational speed 22 of the fan wheel 17 is converted into a first virtual actual rotational speed 46 and into a second virtual actual rotational speed 48. The first virtual actual rotational speed 46 is supplied to the first control unit 24 and the second virtual actual rotational speed 48 becomes the second control unit 26 is supplied.

The control deviation 44 is then determined in a conventional manner in the control units 24, 26 by the difference between the virtual target speed and the virtual actual speed. In this way, different control deviations 44 may be determined for the two control units 24, 26 under certain circumstances.

In principle, several possibilities are conceivable for determining 50 the virtual actual rotational speeds 46, 48. In principle, the virtual actual rotational speeds 46, 48 must be formed from the rotational speed 22 of the fan wheel 17 such that when the rotational speed 22 of the fan wheel 17 corresponds to the target rotational speed 28, the first virtual actual rotational speed 46 of the first virtual target rotational speed 28 and the second actual virtual speed 48 correspond to the second target virtual speed 40. This can ensure that the two control units 24, 26 control the speed 22 of the fan 17 together to the target speed 28.

A first way to determine the virtual actual speeds 46, 48 is to calculate the difference between the desired speed 28 and the virtual target speeds 38, 40 subtract from the speed 22 of the fan 17. As described for example by the following formula: $$\mathrm{virtual\; is}-\mathrm{rotation\; speed}=\mathrm{rotation\; speed}-\left(\mathrm{Should}-\mathrm{rotation\; speed}-\mathrm{virtual\; target}-\mathrm{rotation\; speed}\right)$$

In a further possibility for determining 50 of the virtual actual rotational speeds 46, 48, the same ratio between the rotational speed 22 and the virtual actual rotational speeds 46, 48 is maintained as between the desired rotational speed 28 and the virtual nominal rotational speeds 38, 40. This behavior can be described by the following formula, for example: $$\mathrm{Virtual\; Actual}-\mathrm{rotation\; speed}=\mathrm{rotation\; speed}*\mathrm{virtual\; target}-\mathrm{rotation\; speed}/\mathrm{Should}-\mathrm{rotation\; speed}$$

Both enumerated variants make it possible for both control units 24, 26 to work together and to regulate the rotational speed 22 of the fan wheel 17 to the desired rotational speed 28. Other possibilities for determining 50 of the virtual actual rotational speed 46, 48 are also conceivable as long as the virtual actual rotational speeds 46, 48 coincide with the virtual target rotational speeds 38, 40 when the rotational speed 22 coincides with the target rotational speed 28. Incidentally, the right in the FIG. 3 and FIG. 4 illustrated second embodiment of the method with regard to sequence and function with in the Fig. 1 and Fig. 2 illustrated first embodiment of the method, to the above description, reference is made in this regard.

Claims (14)

1. Method for regulating a rotational speed (22) of a fan wheel (17) to a target rotational speed (28), said fan wheel being driven jointly by a first drive (18) and a second drive (20), wherein the first drive (18) is regulated and/or controlled by a first regulating unit (24) and the second drive (20) is regulated and/or controlled by a second regulating unit (26),
   characterised in that

   - a first torque (34) to be generated by the first drive (18) and a second torque (36) to be generated by the second drive (20) are determined based on an efficiency strategy (32),

   - a first virtual target rotational speed (38) and a second virtual target rotational speed (40) are determined starting from the first torque (34) and the second torque (36),

   - the first virtual target rotational speed (38) is supplied to the first regulating unit (24) as an input variable, and

   - the second virtual target rotational speed (40) is supplied to the second regulating unit (26) as an input variable.
2. Method according to claim 1,
   characterised in that
   an electric motor is used as a first drive (18) and a viscous coupling as a second drive (20) which couples the fan wheel (17) to a shaft (14) of an internal combustion engine (12).
3. Method according to claim 1 or 2,
   characterised in that
   the torques (34, 36) to be generated by the first drive (18) and by the second drive (20) are determined by the efficiency strategy (32) based on a target rotational speed (28) of the fan wheel (17) and/or a rotational speed of the internal combustion engine (12).
4. Method according to any one of claims 1 to 3,
   characterised in that
   the torques (34, 36) to be generated by the first drive (18) and by the second drive (20) are determined by the efficiency strategy (32) taking into account the efficiency level of the first drive (18) and of the second drive (20).
5. Method according to any one of claims 1 to 4,
   characterised in that
   the first virtual rotational speed (38) and the second virtual target rotational speed (40) are determined, using a speed-torque characteristic curve (41) of the fan wheel (17), from the first torque (34) and the second torque (36).
6. Method according to any one of claims 1 to 5,
   characterised in that
   the first regulating unit (24) and the second regulating unit (26) respectively use a pilot control characteristic diagram (27) and a PID controller (25).
7. Method according to claim 6,
   characterised in that
   the first virtual target rotational speed (38) is used as the input variable for the pilot control characteristic diagram (27) of the first regulating unit (24) of the first drive (18), and the second virtual target rotational speed (40) is used as the input variable for the pilot control characteristic diagram (27) of the second regulating unit (26) of the second drive (20).
8. Method according to claim 6 or 7,
   characterised in that
   the control deviation (44) used by the PID controllers (25) is determined from a difference between the rotational speed (22) of the fan wheel (17) and the target rotational speed (28) of the fan wheel (17).
9. Method according to claim 6 or 7,
   characterised in that
   the respective control deviations (44) used by the PID controllers (25) are determined from a difference between the respective virtual target rotational speed (38, 40) and a respective virtual actual rotational speed (46, 48).
10. Method according to claim 9,
    characterised in that

    - the respective virtual actual rotational speeds (46, 48) are determined by subtraction of an offset from the rotational speed (22), wherein the offset is the difference between the target rotational speed (28) and the respective virtual target rotational speed (38, 40).

    - the virtual actual rotational speeds (46, 48) are determined by multiplication of the rotational speed (22) with a division factor, wherein the division factor is the quotient of the respective virtual target rotational speed (38, 40) by the target rotational speed (28).
11. Method according to any one of claims 1 to 10,
    characterised in that
    the first regulating unit (24) and the second regulating unit (26) are rotational speed regulating units.
12. Method according to any one of claims 1 to 11,
    characterised in that
    the rotational speeds of the first drive and of the second drive are coupled.
13. Motor vehicle with a fan (16) driven jointly by a first drive (18) and by a second drive (20), wherein a rotational speed (22) of the fan wheel (17) of the fan (16) is regulated by a method according to any one of claims 1 to 12.
14. Method according to claim 13,
    characterised in that
    the first drive (18) is an electric motor and the second drive (20) is a viscous coupling which couples the fan wheel (17) to an internal combustion engine (12) of the motor vehicle.

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